Dale Collinge told his landlord that after he pulled the rifle’s trigger and a bullet he never knew was inside shattered his girlfriend’s skull, his eyes shifted to the living room couch, where he saw an open box of ammunition.

“And the only thing he thought was, ‘Oh my God, she must have put a real round in,’ ” said Patrick St. Gelais, who owns the Pembroke apartment building where Karen Boelzner was killed Nov. 13, 2011.

The testimony, given yesterday during the trial in Merrimack County Superior Court, offered one possible explanation of how a bullet came to be loaded in the gun that 49-year-old Collinge claims his girlfriend had first pointed at him that night.

The Pembroke man, facing a charge of second-degree murder, told investigators that when 50-year-old Boelzner pulled the trigger, nothing discharged, and he thought the gun was empty when he turned it on her.

His attorneys, who rested their case yesterday without putting Collinge on the stand, have described the incident as a tragic accident. To explain Collinge’s actions – which prosecutors say were reckless and showed extreme disregard for the value of human life – the defense team has looked to Boelzner’s mental state as much as Collinge’s.

Hers, they say, explains his own.

Boelzner had attempted suicide a few months before her death and seemed particularly “agitated” in the few weeks before she died, her sister testified yesterday. Cheryl Martin, who has sat with Collinge’s family and behind the defense table throughout the trial, said her sister tried to kill herself in May 2011, about a week after they held a burial service for their father.

On Nov. 11, 2011, two days before the shooting, the family held a special Mass in their father’s name. Martin said her sister was expected to attend but didn’t.

The sister also said Boelzner had given her a pendant, an item Martin knew held great sentimental value for Boelzner, about a month before her death.

On the night of the shooting, Collinge told investigators about Boelzner’s mood swings, instability and attempt at suicide and wondered if her behavior may have been caused by a bad mix of the four or five medications she was taking. He said that in the moment she pointed the gun at him, he wondered if she was “going through one of her episodes.”

“Especially knowing she’s not in the right state of mind all the times and knowing she’s drinking and maybe she’s looking at me and thinking I’m someone else,” he told investigators.

Prosecutors yesterday, attempting to keep Martin from testifying during the trial, argued that Boelzner’s history of mental illness is irrelevant to the case because they have never disputed Collinge’s claim that she first pointed the gun at him. Before the start of the trial, Judge Richard McNamara seemed to agree and ruled the defense attorneys wouldn’t be allowed to review Boelzner’s medical records.

“He knew that (she was unstable), and he got the gun away from her,” McNamara said. “He had the gun, right?”

But Brown said it doesn’t matter whether self-defense is being raised.

“Because there is no self-defense claim,” McNamara continued. “Your client had the gun.”

“The state has to prove our client’s mood was operating in a particular way,” Brown replied. “That he was aware of the risk, that he consciously – the word consciously is mentioned several times in the jury instructions – he consciously disregarded a known risk. That’s how his brain was operating in those seconds when he had that gun pulled on him and he pulled that gun away.”

What was running through Collinge’s mind is “what this case is entirely about,” Brown argued.

“What’s going on in his brain is he’s looking down the barrel of a rifle (held by) a mentally unstable, suicidal person,” she said.

McNamara decided to let Martin testify, but only to corroborate the points Collinge had raised about Boelzner’s history of mental illness in his interview with investigators.

Psychologist testifies

The defense has argued that when Boelzner pointed the rifle at him, Collinge suffered trauma so severe that he was unaware of his actions in the moments after and unable to accurately create memories of the event.

A psychologist testified on that point yesterday, saying people relate to trauma in one of two ways, either becoming hyper-sensitive and remembering the smallest details or dissociating and taking in only select memories. Philip Kinsler said he believes Collinge falls into the latter category.

As evidence, Kinsler and the defense attorneys have pointed to moments in his interview with investigators in which Collinge wavers over whether he remembers manipulating the bolt and pulling the trigger and describes the incident as a “blur.”

Kinsler said Collinge had reason to be more sensitive to traumatic events because he had experienced trauma earlier in life, likening the phenomenon to the different ways a typical person and someone with combat experience might respond to the sound of a car backfiring.

Kinsler described Collinge’s memory as being similar to a piece of Swiss cheese, and he said Collinge has been futilely trying to create a seamless version of events for the past 18 months.

But Assistant Attorney General Jay McCormack seemed to suggest that the defense attorneys had fabricated the phenomenon.

He said that in an interview with Kinsler and Brown, Collinge said his attorney had told him “not to say that I know” what happened.

“And the defendant also told you during the interview, ‘I’m told to say I’m not sure of anything,’ ” he said to Kinsler.

Kinsler agreed that Collinge had said that.

The quotes were presented with no context. Brown attempted to offer some when she asked Kinsler what he thought Collinge meant when he said he had been told to say he didn’t know what happened.

Kinsler said Collinge was referring to the holes in his memory and saying that he had been advised to not fill in blanks when he really didn’t remember what had happened. Kinsler said Collinge had been doing that while in jail.

“One such scenario he had created was that maybe it was an accident. He stepped back and tripped over the table,” Kinsler said. “And I remember what you said to him was essentially to not keep trying to come up with confabulations, with filling in the blanks.”